Until recently, fixed displacement pumps have conventionally been employed as lubrication oil pumps for internal combustion engines. To prevent possibly damaging oversupply of lubrication oil under some operating conditions, pressure relief valves or other control mechanisms have been used to route the oversupply of oil from the output of the pump back to a reservoir or the pump inlet.
While such systems have proven to be reliable and inexpensive, they suffer from a disadvantage in that energy is used by the pump to pressurize the oversupply of oil which is merely redirected to the pump inlet or reservoir by the control mechanism, and this energy is wasted, reducing the energy efficiency of the pump.
More recently, variable displacement vane pumps have been considered for use as lubrication oil pumps for internal combustion engines. By providing a suitable control mechanism to alter the displacement of the pump to provide only the amount of pressurized lubrication oil necessary for proper operation of the engine, no energy is required to pressurize unneeded oil and thus the energy efficiency of the pump, and the internal combustion engine, can be improved.
However, conventional designs of variable displacement vane pumps have proven to be less energy efficient than desired, especially at high displacement operating conditions.
It is desired to have a variable displacement vane pump which has an improved operating energy efficiency compared to conventional variable displacement vane pumps.